3. Match the level curves with their functions.
f(x,y) = 2x - 7y + 4 matches with _________
f(x,y) = 3y^2 + 4x^2 matches with _________
f(x,y) = x + sin(y) matches with _________
f(x,y) = -3\sqrt{2}x^2 - xy + 2y^2 matches with _________
f(x,y) = y^3 - x^3 matches with _________
f(x,y) = 4xy^2 + xy matches with _________